JPH074989B2 - Thermal recording material - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a heat-sensitive recording sheet, and more specifically, a colorless or slightly pale leuco dye and a color-developing component that develops a color by reacting with the leuco dye under heat. The present invention relates to an improvement of a heat-sensitive recording material in which a heat-sensitive color forming layer contained as is formed on a support.

[Prior art]

The heat-sensitive recording material generally comprises a support such as paper, synthetic paper, or plastic film provided with a heat-sensitive color-forming layer containing a thermo-color-forming composition as a main component, and a thermal head, a thermal pen, a laser beam, a strobe lamp. A colored image can be obtained by heating with, for example. Compared with other recording materials, this type of recording material can obtain recording for a short time with a relatively simple device without performing complicated processing such as development and fixing, has less noise and environmental pollution, and has a low cost. Because of the advantages such as being cheap,
In addition to being used for copying books and documents, it is widely used as a recording material in various fields such as electronic computers, facsimiles, ticket vending machines, labels and recorders.

In recent years, in particular, product information, sales management, systematization of products corresponding thereto, and POS (Point of Sale) system have been advanced, and a heat-sensitive recording material is used as a recording material thereof.

The thermochromic composition used for such a heat-sensitive recording material is generally composed of a color former and a color-developing substance (color developer) capable of coloring the color former under heat. Examples of the color former include lactone, lactam, A colorless or light-colored leuco dye having a spiropyran ring has been conventionally used as a developer, and an organic acid, a phenolic acid substance or the like has been used.

However, this kind of recording material has a light resistance of the image part and the background part, that is, a decrease in the density of the image part when exposed to fluorescent lamps and sunlight for a long time, and the discoloration of the background part is remarkable, especially for the tag for POS system Is not completely satisfactory for the application. As a method of improving the light resistance of these, conventionally, it has been proposed to include an ultraviolet absorber such as benzophenone, benzotriazole, salicylate in the thermosensitive color developing layer, even in this case, satisfactory light resistance Sex has not been obtained. The present inventors, as a result of repeated studies for the purpose of improving the light resistance of the heat-sensitive recording material, have found that a phenolic antioxidant imparts excellent light resistance. It has been found that there are drawbacks such that it easily reacts with the color-forming component inside, causing fog on the background, and poor heat resistance and moisture resistance.

〔Purpose〕

An object of the present invention is to provide a heat-sensitive recording material having excellent light resistance, that is, extremely little image fading or discoloration of the background when exposed to a fluorescent lamp or sunlight for a long time, and excellent in moisture resistance and heat resistance. Especially.

〔Constitution〕

According to the present invention, in a thermosensitive recording material having a thermosensitive coloring layer containing a leuco dye and a developer on a support, a phenylthiourea compound represented by the following general formula (I) is used as a developer. The following general formula (I
There is provided a heat-sensitive recording material comprising an overcoat layer containing a phenolic antioxidant represented by I).

(In the formula, X and Y are each a halogen atom, an alkyl group or a haloalkyl group, and m and n are 0 to 3 respectively.
Represents the integer) (In the formula, R ₁ , R ₂ and R ₃ each independently have 1 to 5 carbon atoms.
In the present invention, the phenolic antioxidant represented by the above general formula contained in the overcoat layer is specifically 1,1-bis (2′-methyl-4′-hydroxy). -5'-t-butylphenyl) butane, 1,1-bis (2'-ethyl-4'-hydroxy-5'-t-butylphenyl) butane, 1,1-bis (2'-butyl-4 ' −
Examples thereof include, but are not limited to, hydroxy-5'-t-butylphenyl) butane.

The overcoat layer usually contains a water-soluble binder, and examples of such a binder include polyvinyl alcohol, carboxyl group-modified polyvinyl alcohol, hydroxyethyl cellulose, methyl cellulose, an isobutylene / maleic anhydride alkali salt, and the like. In addition, polyurethane, styrene / butadiene copolymer, latex such as polyacrylic acid ester, starch and its derivatives, casein,
Examples thereof include a styrene-maleic acid copolymer. Furthermore,
In order to improve water resistance and matching with the thermal head, the overcoat layer contains a water resistant agent, a filler such as a thermosetting organic filler, a higher fatty acid or its ester, an amide or a metal salt, and a lubricant such as a wax. You may let me. Further, a surfactant and the like can be included as appropriate.

The color developer used in the present invention is a phenylthiourea compound represented by the general formula (I).

Specific examples of such a phenylthiourea derivative are as follows:
For example, diphenylthiourea, 4,4'-diethylphenylthiourea, 4,4'-dibutylphenylthiourea, 4,4 '
-Dichlorophenylthiourea, 3,3'-dichlorophenylthiourea, 3,3'-dimethylphenylthiourea, 3,3 '
-Ditrichloromethylphenylthiourea and the like are exemplified, but of course, the present invention is not limited to these.

As the leuco dye used in the present invention, triphenylmethane-based, fluoran-based, phenothiazine-based, auramine-based, spiropyran-based, etc. which are commonly used in this type of heat-sensitive recording material are applied. ,
As a particularly preferable leuco dye, a fluoran compound represented by the following general formula is used.

In the formula, R ₄ and R ₅ are each an alkyl group or a cyclohexyl group, R ₆ is an alkyl group, a haloalkyl group or a halogen atom, R ₇ is a hydrogen atom or a halogen atom, and R ₈ is a hydrogen atom or an alkyl group. is there. As the alkyl group, one having 1 to 8 carbon atoms is usually used.

Examples of the fluorane compound represented by the general formula include 3-diethylamino-7-o-chloro-anilinofluorane, 3-diethylamino-7-m-chloro-anilinofluorane, and 3-di-n-butyl. Amino-7-chloroanilinofluorane, 2- (N-3'-trifluoromethylphenyl) amino-6-diethylaminofluorane, 2- (N-3'-trifluoromethylphenyl-N
-Methyl) amino-6-diethylaminofluorane, 3
-Diethylamino-7- (3'-trifluoromethyl-
4'-chlorophenyl) aminofluorane and the like can be mentioned.

The heat-sensitive color forming layer may further contain a binder, a heat-fusible substance, a filler, a lubricant and the like. A water-soluble polymer is preferably used as the binder. Examples of the water-soluble polymer in this case include polyvinyl alcohol, hydroxyethyl cellulose, methyl cellulose, water-soluble resin of isobutylene / maleic anhydride copolymer alkali salt, polyurethane, styrene / butadiene copolymer, polyacrylic acid ester and the like. Latex or the like can be used. As the filler, calcium carbonate, silica,
Inorganic substances such as titanium oxide, aluminum hydroxide, clay, and talc, as well as organic fillers in which urea-formalin resin, polystyrene, and the like are made into fine particles can be used. Further, if necessary, a surface active agent, a lubricant and the like can be contained in the thermosensitive color developing layer. As the lubricant, various fatty substances such as higher fatty acids or their esters, amides, metal salts, and various wax-like substances can be used.

In order to prepare the above thermal recording material, an aqueous solution containing a leuco dye, the developer represented by the general formula (I) and a binder as a main component is applied on a support such as paper or synthetic paper and dried. Then, a coating solution containing a water-soluble resin, a filler and the phenolic antioxidant represented by the general formula (II) as main components is applied and dried thereon. Here, the amounts of leuco dye, developer and binder used in the thermosensitive coloring layer are appropriately 5 to 30% by weight, 40 to 80% by weight, and 2 to 20% by weight, respectively. It is preferable to use 0.5 to 5 parts by weight, preferably 1 to 3 parts by weight, relative to 1 part by weight of the leuco dye.

In the heat-sensitive recording material of the present invention, an undercoat layer can be provided between the support and the heat-sensitive color forming layer and adjacent to the heat-sensitive color forming layer, whereby sensitivity, whiteness and coating suitability, and further matching can be achieved. It can also be improved. The undercoat layer can be formed with a water-soluble polymer binder, a filler, a lubricant, a surfactant and the like. These things are
What was illustrated above regarding the thermosensitive coloring layer is used.

〔effect〕

The heat-sensitive recording material of the present invention has extremely excellent light resistance,
Further, it has excellent heat resistance and moisture resistance, and gives a recorded image having extremely good storage stability. The heat-sensitive recording material of the present invention is advantageously applied to cargo tags, CADs, labels, etc., which require light resistance, by utilizing such characteristics.

〔Example〕

Examples of the present invention will be shown below. All parts and% shown below are based on weight.

Example 1 [Solution A] 3-di-n-butylamino-7-o-chloroanilinofluorane 10 parts Polyvinyl alcohol 10% aqueous solution 10〃 water 30〃 [Solution B] 3,3'-dichlorophenylthiourea 3.5 Part calcium carbonate 4〃 polyvinyl alcohol 10% aqueous solution 5.5〃 water 17〃 [C liquid] octadecylcarbamoylbenzene 10 parts polyvinyl alcohol 10% aqueous solution 10〃 water 30〃 [D liquid] 1,1-bis (2'-methyl-4) ′ -Hydroxy-5′-
t-Butylphenyl) butane 10 parts Polyvinyl alcohol 10% aqueous solution 10 〃 silica 10 〃 water 30 parts The above composition is crushed and dispersed by a ball mill so that the average particle size becomes 5 μm or less, and then [A] to [D]. ] Liquid was obtained. 10 parts of [solution A] thus obtained, 30 parts of [solution B] and [C]
Liquid] was mixed with 30 parts, and the mixed liquid was applied and dried on a high-quality paper having a basis weight of 50 g / m ^{2 so} that the dry adhesion amount was 0.5 g / m ^{2 in} terms of dye, and a thermosensitive coloring layer was formed. Next, the [D liquid] was coated on the thermosensitive coloring layer with a wire bar so that the dry adhesion amount was 4 g / m ² , to obtain a thermosensitive recording material of the present invention.

Examples 2 and 3 In Example 1, the antioxidant of [D liquid] was 1,1-bis (2'-ethyl-4'-hydroxy-5'-t-butylphenyl) butane (Example 2) and 1,1-bis (2'-
A heat-sensitive recording material of the present invention was obtained in the same manner except that butyl-4'-hydroxy-5'-t-butylphenyl) butane (Example 3) was used instead.

Comparative Example 1 A sample for comparison was obtained in the same manner as in Example 1 except that the phenolic antioxidant was removed from [D liquid] and the overcoat layer containing no antioxidant was provided.

Comparative Example 2 In the same manner as in Example 1, [E liquid] having the following composition was prepared.

[E liquid]

Octadecylcarbamoylbenzene 10 parts 1,1-bis (2'-methyl-4'-hydroxy-5'-
t-Butylphenyl) butane 10 〃 polyvinyl alcohol 10% aqueous solution 10 〃 water 30 〃 Next, [A solution] 10 parts, [B solution] 30 parts and [E solution] 30 parts were mixed, and this mixed solution was dried. The weight per hour is 0 in leuco dye conversion.
A thermal recording material was obtained by coating and drying on a high-quality paper having a basis weight of 50 g / m ² using a wire bar so that the weight became 5 g / m ² .

Comparative Example 3 A comparative sample was obtained in the same manner as in Example 1 except that bisphenol A was used instead of 3,3′-dichlorophenylthiourea in [B liquid].

Next, each of the heat-sensitive recording materials obtained above is subjected to the following various tests. The results are shown in Table-1.

Heat resistance: The colored part and the background part, which are colored at 110 ° C using a thermal gradient tester, are left in a 60 ° C dry atmosphere for 24 hours,
The density change in the image area and the density change in the background area at that time were measured with a Macbeth densitometer.

Moisture resistance: Using a thermal gradient tester, leave the colored part and the background part colored at 110 ° C in an atmosphere of 40 ° C and 90% RH for 24 hours, and then change the density of the image part and the background part. The change in concentration was measured by a Macbeth densitometer.

Sunlight fading: The colored part and the background part, which were colored at 110 ° C using a thermal gradient tester, were exposed to sunlight for 30 hours, and the density change in the image part and the background part were measured with a Macbeth densitometer. It was measured at.

Fading of fluorescent lamps: The color-developed area and the background area colored at 110 ° C using a thermal gradient tester were exposed to a fluorescent light of 5000 Lux for 240 hours, and the density change in the image area and the density change in the background area at that time Was measured with a Macbeth densitometer.

Claims (1)

[Claims] 1. A thermosensitive recording material comprising a support and a thermosensitive coloring layer containing a leuco dye and a developer, wherein a phenylthiourea compound represented by the following general formula (I) is used as the developer and the thermosensitive coloring material is used. A heat-sensitive recording material comprising an overcoat layer containing a phenolic antioxidant represented by the following general formula (II) on the color forming layer. (In the formula, X and Y are each a halogen atom, an alkyl group or a haloalkyl group, and m and n are 0 to 3 respectively.
Represents the integer) (In the formula, R ₁ , R ₂ and R ₃ each independently have 1 to 5 carbon atoms.
Represents the alkyl group of